U.S. patent application number 10/231499 was filed with the patent office on 2004-05-20 for micro-electromechanical voltage converter.
Invention is credited to Koeneman, Paul B..
Application Number | 20040095031 10/231499 |
Document ID | / |
Family ID | 32296777 |
Filed Date | 2004-05-20 |
United States Patent
Application |
20040095031 |
Kind Code |
A1 |
Koeneman, Paul B. |
May 20, 2004 |
Micro-electromechanical voltage converter
Abstract
The invention concerns a method and device for using a homopolar
machine to convert a first DC voltage to a second DC voltage.
According to the method, the invention can include the steps of
applying a first DC voltage between an inner and outer radial
portion of a primary conductive disc comprising a rotor to produce
an electric current, applying a magnetic field aligned with an axis
of the rotor to induce a rotation of the rotor about the axis
responsive to the electric current, and coupling the rotation of
the rotor to at least one secondary conductive disc disposed in the
magnetic field to produce at least a second DC voltage between an
inner and outer radial portion of the secondary conductive disc or
discs.
Inventors: |
Koeneman, Paul B.; (Palm
Bay, FL) |
Correspondence
Address: |
SACCO & ASSOCIATES, PA
P.O. BOX 30999
PALM BEACH GARDENS
FL
33420-0999
US
|
Family ID: |
32296777 |
Appl. No.: |
10/231499 |
Filed: |
November 18, 2002 |
Current U.S.
Class: |
310/100 |
Current CPC
Class: |
H02K 47/14 20130101;
H02K 31/00 20130101; H02M 3/00 20130101; H02M 3/003 20210501 |
Class at
Publication: |
310/100 |
International
Class: |
H02K 007/10; H02P
015/00; H02K 049/00 |
Claims
1. A method for converting a first DC voltage to a second DC
voltage using a homopolar machine comprising the steps of: applying
a first DC voltage between an inner and outer radial portion of a
primary conductive disc comprising a rotor to produce an electric
current; applying a magnetic field aligned with an axis of said
rotor to induce a rotation of said rotor about said axis responsive
to said electric current; and coupling said rotation of said rotor
to a secondary conductive disc disposed in said magnetic field to
produce a second DC voltage between an inner and outer radial
portion of said secondary conductive disc.
2. The method according to claim 1 further comprising the step of
controlling a ratio of said first DC voltage to said second DC
voltage by selectively controlling the strength of said magnetic
field applied to at least a portion of one of said conductive
discs.
3. The method according to claim 1 further comprising the step of
controlling a ratio of said first DC voltage to said second DC
voltage by selectively controlling a radial spacing between said
inner and outer radial portions of said secondary conductive disc
relative to said inner and outer radial portion of said primary
conductive disc.
4. The method according to claim 1 further comprising the step of
axially aligning said secondary conductive disc with said primary
conductive disc.
5. The method according to claim 4 further comprising the step of
coupling said rotation of said rotor to said secondary conductive
disc through a common axle.
6. The method according to claim 1 further comprising the step of
applying said magnetic field by positioning at least one permanent
magnet adjacent to said rotor.
7. The method according to claim 1 further comprising the step of
applying said magnetic field by positioning at least one
electro-magnet adjacent to said rotor.
8. The method according to claim 7 further comprising the step of
controlling a ratio of said first DC voltage to said second DC
voltage by selectively controlling an electric current applied to
said at least one electro-magnet.
9. The method according to claim 1 further comprising the step of
selectively applying a different intensity magnetic field outside a
perimeter of a smaller one of said conductive discs as compared to
inside said perimeter so as to control a ratio of said first DC
voltage to said second DC voltage.
10. The method according to claim 1 further comprising the step of
fabricating said rotor on a substrate
11. A micro-electromechanical homopolar device for converting a
first DC voltage to a second DC voltage comprising: a primary
conductive disc rotatably mounted on a substrate; DC voltage input
leads integrated with said substrate and coupled to a primary set
of brushes for applying said first DC voltage between an inner and
outer radial portion of said primary conductive disc to produce an
electric current; a magnetic field source producing a magnetic
field aligned for causing a rotation of said primary conductive
disc responsive to said electric current; a secondary conductive
disc mechanically coupled to said primary conductive disc for
rotation responsive to said rotation of said primary conductive
disc, and disposed within said magnetic field for generating said
second DC voltage responsive to said rotation; and DC voltage
output leads coupled to a secondary set of brushes forming an
electrical connection to an inner and outer radial portion of said
secondary conductive disc.
12. The device according to claim 11 wherein said primary and
secondary conductive discs have a common axis of rotation.
13. The device according to claim 11 wherein said secondary
conductive disc secondary disc is formed as an integral part of the
primary conductive disc.
14. The device according to claim 11 wherein said magnetic field is
aligned parallel with an axis of rotation for each of said primary
and secondary conductive discs.
15. The device according to claim 11 wherein said magnetic field
for at least a portion of one of said primary and secondary
conductive discs has an intensity that is different as compared to
an intensity field applied to at least a portion of the other one
said primary and secondary conductive discs.
16. The device according to claim 11 further comprising a control
circuit coupled to said magnetic field source for selectively
controlling an intensity of said magnetic field applied
respectively to at least a portion of one of said conductive
discs.
17. The device according to claim 11 wherein a diameter of said
primary conductive disc is a different size as compared to a
diameter of said secondary conductive disc.
18. The device according to claim 11 wherein said substrate is at
least one of a ceramic and a semiconductor substrate and at least
one of said conductive discs rotates within a circular recess
formed within said substrate.
19. The device according to claim 11 wherein said primary and
secondary conductive discs are electrically isolated by an
insulator.
20. A homopolar device for converting a first DC voltage to a
second DC voltage comprising: a primary conductive disc rotatably
mounted in a support structure; a primary set of brushes for
applying said first DC voltage between an inner and outer radial
portion of said primary conductive disc to produce an electric
current; a magnetic field source producing a magnetic field aligned
for causing a rotation of said primary conductive disc responsive
to said electric current; a secondary conductive disc mechanically
coupled for rotation responsive to said rotation of said primary
conductive disc, and disposed within said magnetic field for
generating said second DC voltage responsive to said rotation; and
a secondary set of brushes forming an electrical connection to an
inner and outer radial portion of said secondary conductive
disc.
21. The device according to claim 20 wherein said primary and said
secondary conductive discs rotate within a circular recess formed
in a planar substrate.
22. The device according to claim 21 wherein said planar substrate
is formed from a material selected from the group consisting of a
semiconductor and a ceramic.
23. The device according to claim 20 wherein said primary
conductive disc and said secondary conductive disc have a common
axis of rotation.
24. The device according to claim 20 wherein said secondary
conductive disc secondary disc is formed as an integral part of the
primary conductive disc.
25. The device according to claim 20 wherein said magnetic field is
aligned parallel with an axis of rotation for each of said primary
and secondary conductive discs.
26. The device according to claim 20 wherein said magnetic field
for at least a portion of one of said primary and secondary
conductive discs has an intensity that is different as compared to
an intensity field applied to at least a portion of the other one
said primary and secondary conductive discs.
27. The device according to claim 20 further comprising a control
circuit coupled to said magnetic field source for selectively
controlling an intensity of said magnetic field applied
respectively to at least a portion of one of said conductive
discs.
28. The device according to claim 20 wherein a diameter of said
primary conductive disc is a different size as compared to a
diameter of said secondary conductive disc.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Statement of the Technical Field
[0002] The inventive arrangements relate generally to methods and
apparatus for providing voltage conversion, and more particularly
efficient variable DC to DC voltage conversion in a small
volume.
[0003] 2. Description of the Related Art
[0004] Conversion of a first DC voltage to second DC voltage has
always been problematic. Unlike AC voltages that can be efficiently
stepped up or down using simple transformers, circuits for
converting DC voltages are generally more complex. Such systems
tend to occupy a large volume, have noise problems, and/or operate
relatively inefficiently. For example, one approach for solving the
DC to DC conversion problem is the DC-AC-AC-DC converters. In such
systems, a DC voltage is first converted to an AC voltage, then
stepped up or down using conventional AC transformer techniques,
and finally converted back to DC. This approach is relatively
expensive and requires transformers that can add weight and bulk to
a design.
[0005] Buck and Boost type switching converters can also be used
for DC voltage conversion. However, each of these designs also
suffers from problems. Pulsating input currents in Buck converters
tend to send too much noise back to the source. Also, these devices
tend to suffer from poor line regulation. Similarly, pulsating
output currents with Boost converters are known to result in noise
problems.
[0006] Another approach that has been used to solve the DC to DC
conversion problem makes use of a Single-Ended Primary Inductance
Converter (SEPIC). However, the SEPIC device also tends to suffer
from noise problems. Further, these converters can suffer from
reduced efficiencies at lower voltages. Accordingly, there is a
need for compact variable DC to DC voltage conversion system that
efficiently converts DC voltages with low noise and good
isolation.
[0007] Homopolar machines are well known in the art. For example,
several variations of such machines are described in U.S. Pat. No.
5,530,309 to Weldon, U.S. Pat. No. 5,481,149 to Kambe, U.S. Pat.
No. 5,587,618 to Hathaway. These patents describe the use of a
homopolar generator for producing high current, low voltage energy
for various applications. U.S. Pat. No. 6,051,905 to Clark
describes a homopolar machine for use in conjunction with storage
batteries for an electric car. In general, however, such references
have not applied homopolar machines to the problem of converting
one DC voltage to a second DC voltage.
[0008] U.S. Pat. No. 5,821,659 to Smith describes a homopolar
transformer for conversion of electrical energy. However, the
device is mechanically complex and therefore relatively unsuited
for micro-electronic fabrication on a substrate.
SUMMARY OF THE INVENTION
[0009] The invention concerns a method and device that makes use of
a homopolar machine for converting a first DC voltage to a second
DC voltage. According to the method, the invention can include the
steps of applying a first DC voltage between an inner and outer
radial portion of a primary conductive disc comprising a rotor to
produce an electric current, applying a magnetic field aligned with
an axis of the rotor to induce a rotation of the rotor about the
axis responsive to the electric current, and coupling the rotation
of the rotor to at least one secondary conductive disc disposed in
the magnetic field to produce at least a second DC voltage between
an inner and outer radial portion of the secondary conductive disc
or discs.
[0010] The method can also include the step of controlling a ratio
of the first DC voltage to the second DC voltage by selectively
controlling the strength of the magnetic field applied to at least
a portion of one of the conductive discs. Alternatively, or in
addition thereto, the method can comprise the step of controlling a
ratio of the first DC voltage to the second DC voltage by
selectively controlling a radial spacing between the inner and
outer radial portions of the secondary conductive disc or discs
relative to the spacing between the inner and outer radial portion
of the primary conductive disc.
[0011] The method can be carried out by axially aligning the
secondary conductive disc or discs with the primary conductive
disc, and coupling the rotation of the rotor to the secondary
conductive discs, for example through a common axle. The magnetic
field can be applied by positioning at least one permanent magnet
adjacent to the rotor. Alternatively, or in addition thereto the
magnetic field can be applied by positioning one or more
electromagnets adjacent to the rotor. A ratio of the first DC
voltage to the second DC voltage can be controlled by selectively
controlling an electric current applied to the electromagnets.
[0012] According to one aspect of the invention, a different
intensity magnetic field can be selectively applied outside a
perimeter of a smaller one of the conductive discs as compared to
inside the perimeter so as to control a ratio of the first DC
voltages to the second DC voltage or voltages.
[0013] The invention can also include a device, for example a
micro-electromechanical device for converting a first DC voltage to
a second DC voltage or voltages. The device can include a primary
conductive disc rotatably mounted to a rotor support structure. DC
voltage input leads can be provided integrated with the substrate
and coupled to a primary set of brushes for applying the first DC
voltage between an inner and outer radial portion of the primary
conductive disc to produce an electric current. A magnetic field
source is provided for producing a magnetic field aligned for
causing a rotation of the primary conductive disc responsive to the
electric current. One or more secondary conductive discs is
mechanically coupled to the primary conductive discs for rotation
responsive to the rotation of the primary conductive disc. A
diameter of the primary conductive disc can be the same size or
different size as compared to a diameter of the secondary
conductive disc(s). An insulator preferably electrically isolates
the primary and secondary conductive discs. The secondary
conductive disc(s) can also be disposed within the magnetic field
for generating the second DC voltage responsive to the rotation. DC
voltage output leads are provided coupled to secondary set of
brushes forming an electrical connection to an inner and outer
radial portion of the secondary conductive disc. If the device is
formed as a micro-electromechanical device, the substrate can be a
ceramic or semiconductor material.
[0014] The magnetic field is aligned parallel with an axis of
rotation for each of the primary and secondary conductive discs.
According to one aspect of the device, the primary and secondary
conductive discs can have a common axis of rotation. According to
another aspect of the invention, the magnetic field for at least a
portion of one of the primary and secondary conductive discs can
have an intensity that is different as compared to an intensity
field applied to the other one of the primary and secondary
conductive discs.
[0015] A control circuit can be provided coupled to the magnetic
field source for selectively controlling the intensity of the
magnetic field applied respectively to at least a portion of each
of the conductive discs. For example, the control circuit can
control a current applied to an electromagnet for controlling the
field intensity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a partial cross-sectional view of a DC to DC
homopolar voltage conversion device.
[0017] FIG. 2 is a top view of the device of FIG. taken along line
2-2.
[0018] FIG. 3 is a top view of a first alternative embodiment of
the invention.
[0019] FIG. 4 is a side view of the first alternative embodiment of
FIG. 3.
[0020] FIG. 5 is a side view of a second alternative embodiment of
the invention.
[0021] FIG. 6 is a top view of the embodiment of FIG. 5
[0022] FIG. 7a-7h is a series of drawings useful for understanding
how the device in FIGS. 1 and 6 can be fabricated in a silicon
substrate.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] A homopolar machine for converting a first DC voltage to a
second DC voltage is illustrated in FIGS. 1 and 2. The device 100
includes a primary conductive disc 104 rotatably mounted on a
support structure 101. The support structure is preferably a
ceramic or semiconductor substrate but the invention is not so
limited. According to one aspect of the invention, the support
structure can comprise a portion of a planar circuit board or
semiconductor device on an integrated circuit and the primary
conductive disc can be mounted within a circular recess 118 formed
within the substrate.
[0024] The primary conductive disc 104 can rotate about a fixed
rotor support 102 or, in an alternative configuration, the rotor
support 102 can be fixed to the primary conductive disc 104 and the
entire assembly can rotate in a bushing 116. DC voltage input leads
106a and 106b are provided and can be integrated with the substrate
forming the support structure 101. The input leads preferably form
a conductive contact with a primary set of brushes 108a and 108b
respectively. Brush 108a can be integrated with the rotor support
102 or may be formed adjacent thereto. Brush 108b is preferably
formed at or near an outer peripheral portion of a circular recess
118. In this way, a first DC voltage Vin can be applied between an
inner 110 and outer 112 radial portion of the primary conductive
disc 104 to produce an electric current fin. Notably, the location
of the brushes 108a and 108b are shown making contact with the
primary conductive disc 104 at an extreme inner and outer radial
portion thereof, the invention is not so limited and other
configurations are also possible.
[0025] A magnetic field source 114 can be provided for producing a
magnetic field 122 aligned as shown in FIG. 1 for causing a
rotation of the primary conductive disc 104 responsive to the
electric current lin. The magnetic field source 114 can be
comprised of a permanent magnet or an electromagnet positioned
adjacent to the conductive disc 104 as shown. Alternatively, or in
addition thereto, a magnetic field source 115 can be provided below
the primary conductive disc 104 as shown. Magnetic field source 115
can likewise comprise a permanent magnet or electromagnet.
[0026] At least one secondary conductive disc 120 is preferably
provided and mechanically coupled to the primary conductive discs
104 for rotation responsive to the rotation of the primary
conductive disc. As best seen in FIG. 1, the primary and secondary
conductive discs can have a common axis of rotation 121. A diameter
of the primary conductive disc 104 can be the same or different as
compared to a diameter of the secondary conductive disc 120. The
relative diameter of the conductive discs 104, 120 can be used as
one means for controlling the ratio of the input voltage Vin to the
output voltage Vout. For a given magnetic field intensity and
rotational velocity, a smaller diameter secondary conductive disc
120 will generally produce a lower output voltage.
[0027] The primary and secondary conductive discs are preferably
electrically isolated from one another by an insulating layer 124.
The insulating layer 124 isolates the input voltage V.sub.in from
the output voltage V.sub.out. The insulating layer 124 also
provides current isolation between the primary and secondary discs.
Nonetheless, the insulating layer 124 is not necessary in all
applications. As best seen in FIG. 1, the secondary conductive disc
120 can also be disposed within the magnetic field 122.
Consequently, when the rotation of primary conductive disc 104 is
coupled to secondary conductive disc 120, the secondary conductive
disc will generate a second DC voltage Vout responsive to the
rotation.
[0028] DC voltage output leads 126a and 126b form an electrical
contact with a secondary set of brushes 128a, 128b. The brushes
provide an electrical connection to an inner and outer radial
portion respectively of the secondary conductive disc 120. Brush
128a can be integrated with or can be positioned adjacent to the
rotor support 102. Brush 128b is preferably formed at or near an
outer peripheral portion of a circular recess 130. Notably, the
location of the brushes 128a and 128b are shown making contact with
the secondary conductive disc 104 at an extreme inner and outer
radial portion thereof, but the invention is not so limited and
other configurations are also possible.
[0029] Notably, while only a single secondary conductive disc 120
is shown in FIG. 1, the invention is not so limited. Thus,
additional secondary conductive discs can be stacked above or below
the primary conductive disc 104 in a manner similar to the
arrangement shown with respect to conductive disc 120. Each of the
secondary conductive discs 120 can have associated brushes 128a,
128b. The additional secondary conductive discs can be of various
diameters as may be appropriate for producing selected DC output
voltages.
[0030] According to one aspect of the invention, the magnetic field
source 114, 115 can be configured to produce a magnetic field 122
that is generally constant with time and over the entire area
circumscribed by the outermost perimeter of the conductive discs
104, 120. However, the invention is not so limited. For example,
one or both of the magnetic field sources 114, 115 can be
configured to produce a more or less intense magnetic field over a
selected portion of the area occupied by one of the conductive
discs to control the ratio over the input and output voltage.
[0031] For example, one or both of the magnetic field sources 114,
115 can be configured so that the magnetic field 122 is of a
greater intensity in an annular area 130 defined between the outer
perimeter of the secondary conductive disc 120 and the outer
perimeter of the primary conductive disc 104. In FIGS. 1 and 2, an
increase of magnetic flux density in this area can be used to
increase the rate of rotation for the primary conductive disc 104
for a constant input current. This will cause a corresponding
increase in the rate of rotation of the secondary conductive disc,
and this increased rotational velocity will cause an increase in
voltage output from the secondary conductive disc. if one or both
of the magnetic field sources 114, 115 is an electromagnet, the
intensity of the magnetic field in selected areas can be varied
over time to control the voltage output from the secondary
conductive disc 120. Control circuitry 132 can be provided for
selectively controlling the field intensity produced by the
electromagnets in the selected regions. For example, the control
circuit can control a current applied to an electromagnet for
controlling the field intensity. In another arrangement,
microactuators can be provided to physically move a permanent
magnet closer to, or farther from, the rotor to vary the field
intensity at the rotor. For example, a microelectromechanical
actuator can be provided. In particular, an electrostatic actuator
can be used when a voltage controlled actuator is desired, or a
thermal actuator can be used when a current controlled actuator is
desired. Both types of actuators are known to the skilled
artisan.
[0032] FIGS. 1 and 2 illustrate one configuration by which the
primary conductive disc can be mechanically coupled to the
secondary conductive disc for imparting a rotational moment.
However, it should be understood that the invention is not so
limited. Instead, the invention is intended to encompass any of a
wide variety of possible mechanical arrangements by which the first
conductive disc can transfer a rotational moment to the secondary
conductive disc. These can include, without limitation, gear
drives, belt drives, and hydraulic drive systems. For example, an
alternative embodiment of the invention is illustrated in FIGS. 3
and 4.
[0033] Similar to the previously described embodiment of FIGS. 1
and 2, the rotational energy of the device in FIGS. 3 and 4 can be
coupled from a primary conductive disc 104' to a secondary
conductive disc 120' by means of a radial edge drive system. More
particularly, the peripheral edge of the primary conductive disc
can be positioned to engage a peripheral edge of the secondary
conductive disc. In this configuration, counter-clockwise rotation
of the primary conductive disc will result in a clockwise rotation
of the secondary conductive disc.
[0034] In FIGS. 3 and 4, each of the conductive discs can be
exposed to a magnetic field B1, B2 as illustrated in FIG. 4. The
fields B1 and B2 can be the same or different intensity. Thus, the
arrangement of FIGS. 3 and 4 can permit the ratio of the input to
output voltage to be controlled by simply varying the relative
strength of each of the magnetic fields B1, B2. The configuration
in FIGS. 3 and 4 is more versatile in some respects as compared to
the embodiment in FIGS. 1 and 2 because the side-by-side
configuration provides greater capacity for varying the voltage
ratio since the magnetic field can be varied over the entire rotor
rather than just an outer annulus. Further, the input and output
voltages are not referenced to one another when there is an
insulating layer at the outer radius of one or more rotors.
[0035] FIGS. 5 and 6 illustrate an alternative embodiment of the
invention in which the secondary disc 505 is formed as an integral
part of the primary conductive disc 504. In this arrangement, the
primary conductive disc 504 is rotatably mounted within a circular
recess 506 of the substrate 502 in a manner similar to that
described relative to FIGS. 1 and 2. A magnetic field source 512 is
used to produce a magnetic field 510 that is aligned with the axis
of rotation of conductive disc 504. A primary set of brushes 508a
and 508b can be fixed respectively at an inner and outer radial
portion of the conductive disc and define the working radius of the
primary conductive disc 504. A third brush 508c is provided that
can be moved radially across the surface of the primary conductive
disc. The third brush 508c and one of the fixed brushes, such 508a,
can comprise the secondary set of brushes, 508a being a shared
brush. The position of the movable brush 508c relative to fixed
brush 508b defines inner and outer radial portions of the secondary
conductive disc 505 and the working radius of the secondary
conductive disc 505.
[0036] The movable brush 508c can be implemented by any suitable
means. For example the movable brush 508c can be mounted on a
slider with a microactuator. For example, an electrostatic actuator
or a thermal actuator can be used.
[0037] With the arrangement described above in FIGS. 5 and 6, an
input voltage at V1 applied between brushes 508a and 508b will
cause a rotation of the conductive disc 504. This rotation will
cause a voltage V2 to be induced between brushes 508a and 508c. The
ratio of V1 to V2 will be determined by the relative spacing
between 508a and 508b as compared to the spacing between 508a and
508c. In one arrangement, the magnetic field strength between
brushes 508b and 508c can be varied relative to the magnetic field
strength between brushes 508a and 508c, or vice versa, to produce a
variable voltage ratio. The ratio V2/V1 is equal to the percentage
of the total magnetic flux passing inside the radius of 508c
505.
[0038] The foregoing FIGS. 1-6 illustrate three possible
configurations in which a homopolar device can be implemented to
convert one DC voltage to a second DC voltage. Those skilled in the
art will recognize that the invention is not limited to those
specific embodiments shown. Similarly, these devices can also serve
as current converters. At steady state, the output power will equal
the input power (minus a small amount of parasitic loss). This
means if the output voltage is half the input voltage, the output
current will be approximately twice the input current.
[0039] According to a preferred embodiment, the invention can be
implemented as a micro-electronic machine formed in a ceramic or
semiconductor substrate. For example, low temperature co-fired
ceramic (LTCC), silicon, gallium arsenide, gallium nitride,
germanium, indium phosphide, or any other substrate material
suitable for a micro-electromechanical manufacturing process can be
used to manufacture the invention. In particular, the simple
structure of the devices is uniquely well suited Polysilicon
microfabrication, which is well known to those skilled in the art.
One such technique is disclosed in David A. Koester et al., MUMPs
Design Handbook (Rev. 7.0, 2001). An exemplary polysilicon
microfabrication process is shown in FIGS. 7a-7h. It should be
noted, however, that the invention is not limited to the process
disclosed herein and that other ceramic and semiconductor
microfabrication processes can be used. Further, FIGS. 7a-7h
correspond to the fabrication of the device in FIGS. 1 and 2 but it
will be understood that similar techniques could be used for the
devices in FIGS. 3-6.
[0040] Referring now to FIG. 7a, a first silicon substrate layer
(first silicon layer) 702 can be provided to begin forming a wafer
structure for the micro-electromechanical voltage converter, for
example, a silicon wafer typically used in IC manufacturing. It may
be desirable for the first silicon layer 702 to have electrically
insulating properties. Accordingly, the first silicon layer 702 can
be formed without doping or have only a light doping.
Alternatively, an electrically insulating layer can be applied over
the first silicon layer 702. For example, a layer of silicon
dioxide can be applied over the first silicon layer 702. A
conductive layer can be deposited onto the substrate, from which
circuit traces 704 can be etched. For example, a conductive layer
of doped polysilicon or aluminum can be deposited onto the
substrate. After deposition of the conductive layer, conductive
traces 704 can be defined using known lithography and etching
techniques.
[0041] After the circuit traces are formed, an electrically
insulating layer 710, such as silicon nitride (SiN), can be
deposited over the first substrate and circuit traces. For example,
low pressure chemical vapor deposition (LPCVD) involving the
reaction of dichlorosilane (SiH2Cl2) and ammonia (NH3) can be used
to deposit an insulating layer. A typical thickness for the SiN
layer is approximately 600 nm.
[0042] Vias 706 then can be formed through the insulating layer 710
and filled with electrically conductive material (e.g. Aluminum) to
electrically contact the circuit traces 704 at desired locations.
Contact brushes 708 then can be deposited on the vias 706 so that
the contact brushes 708 can be electrically continuous with the
respective vias 706. Accordingly, the electrical contact brushes
are electrically continuous with respective ones of circuit traces
704. Two axial contact brushes and two radial edge contact brushes
are shown in the figure, but additional axial and radial edge
contact brushes can be provided. Further, the contact brushes can
include any conductive material suitable for use in a contact
brush, for example a carbon nano composite, which can be applied
using a thermo spray method commonly known to the skilled artisan.
In another arrangement the contact brushes can be a conductive
liquid.
[0043] A first structural layer of polysilicon (poly 1) 712 can be
deposited onto the insulating layer 710 using LPCVD. The poly 1
layer then can be etched to form a radial aperture 711 which
exposes the contact brushes. In an alternate arrangement, the
aperture region can be masked prior to application of the poly 1
layer 712, thereby preventing deposition in the aperture
region.
[0044] Referring to FIG. 7b, a first sacrificial layer 713, for
example silicon dioxide (SiO.sub.2) or phosphosilicate glass (PSG),
can be applied to the substrate over the previously applied layers.
The first sacrificial layer 713 is removed at the end of the
process, as is further discussed below. The sacrificial layer can
be deposited by LPCVD and annealed to the circuit. For example, in
the case that phosphosilicate glass (PSG) is used for the
sacrificial layer, the sacrificial layer can be annealed at
1050.degree. C. in argon. The first sacrificial layer 713 then can
be planarized within the aperture 711 using a planarizing etch-back
process to form a flat base within the aperture 711 that is
recessed from an upper elevation of the first sacrificial
layer.
[0045] Referring to FIG. 7c, a first conductor then can be
deposited into the aperture 711 to form a first conductive disc
(first disc) 714 having opposing upper and lower surfaces. Further,
the first disc 714 can be wholly contained within the aperture 711
so that the only material contacting the first disc 714 is the
sacrificial layer 713. The thickness of the first disc 714 can be
determined by the thickness of the first sacrificial layer 713 and
the amount of etch-back applied to the aperture 711.
[0046] Referring to FIG. 7d, a second conductor can be deposited
onto the first disc 714 to form a conductive disc (second disc) 718
to form a rotating assembly 719. Notably, mechanical
characteristics, such as rigidity, should be considered when
selecting a thickness of the rotating assembly 719. Further, in one
arrangement, an insulator layer 716, for example SiN, can be formed
over the first disc 714 prior to the deposition of the second disc
718. Importantly, the insulator layer 716 can provide voltage and
current isolation between the first disc 714 and the second disc
718.
[0047] A second aperture 720 then can be etched through an axial
region of the rotating assembly 719 and through the first
sacrificial layer below the center of the disc to expose the
electrically insulating layer 710, as shown in FIG. 7e. The second
aperture 720 can be sized to form a hole in the rotating assembly
719 having a radius equal to or smaller than the radial distance
between opposing inner most contact brushes 708. Known etching
techniques can be used, for example reactive ion etch (RIE), plasma
etching, etc. A second sacrificial layer 722, for example SiO.sub.2
or PSG, then can be deposited over all exposed surfaces of the
rotating assembly 719. Importantly, a region of the electrically
insulating layer 710 should be masked during the application of the
second sacrificial layer 722 to prevent the second sacrificial
layer 722 from adhering to the electrically insulating layer 710
within the second aperture 720. Alternatively, a subsequent etching
process can be performed to clear away the second sacrificial layer
from the electrically insulating layer 710.
[0048] In FIG. 7f, using LPCVD, a second layer of polysilcon (poly
2) 724 can be deposited over the previously applied layers, for
example the poly 1 layer 712 surrounding the first disc 714,
thereby adding an additional silicon structure. Notably, the poly 2
layer 724 also can fill the second aperture 720. A washer shaped
region then can be etched to remove a washer shaped portion of the
poly 2 layer located above the rotating assembly 719. Notably, the
inner radius of the washer shaped region can be larger than the
inner radius of the rotating assembly 719. Accordingly, the etching
of the poly 2 layer 724 can leave a structure 725, having a "T"
shaped cross section, within the second aperture 720. An upper
portion of the structure 725 can extend over the inner portion of
the rotating assembly 719, thereby limiting vertical movement of
the rotating assembly 719 once the sacrificial layers are removed.
Further, the structure 725 can operate as a bearing around which
the rotating assembly 719 can rotate. Alternatively,
electromagnetic or electrostatic bearings can be provided in the
second aperture 720.
[0049] Referring to FIG. 7g, the first and second sacrificial
layers 713 and 722 then can be released with a hydrogen fluoride
(HF) solution as is known to the skilled artisan. For example, the
wafer structure 726 can be dipped in an HF bath. HF does not attack
silicon or polysilicon, but quickly etches SiO2. Notably, the HF
can etch deposited SiO2 approximately 100.times. faster than SiN.
The release of the sacrificial layers 713 and 722 enables the
rotating assembly 719, and in particular the first disc 714, to
rest upon, and make electrical contact with, contact brushes 708.
Moreover, the release of the sacrificial layers 713 and 722 frees
the rotating assembly 719 to rotate about its axis.
[0050] A second wafer structure 728 is aligned with the wafer
structure 726 for final assembly. The second wafer structure
includes brushes 730 and 731 and conductive trace layers 732, which
can be formed in the same manner as equivalent layers in the first
wafer structure 716. Importantly, the contact brushes 730 and 731
can be positioned to electrically contact the second disk 718 of
the rotating assembly 719 when the second wafer structure 728 is
assembled to the first wafer structure 726. Further, the bonding of
the second wafer structure 728 to the first wafer structure 726 can
provide an enclosed region in which the rotating assembly 719 can
rotate. In particular, the enclosed region can be sealed to keep
out dust and other contaminants, which can reduce the efficiency of
the micro-electromechanical voltage converter.
[0051] The assembly is completed in by securing a magnet layer 734
over the disc assembly as shown. The magnet 734 can be fixed above
and/or below the rotating assembly 719 to provide a magnetic field
aligned with the axis of rotation of the rotating assembly 719. For
example a magnet can be attached to the top of the second wafer
structure 728. Further, a magnet can be attached to the bottom of
the first wafer structure 726, for example with a third silicon
substrate layer.
* * * * *